This application claims the priority of Japanese patent application Serial No. PP 251950 filed on Sep. 6, 1999.
The present invention relates to a shadow mask for a Braun tube (cathode-ray tube), a plate member for the shadow mask and a method of manufacturing the shadow mask. More particularly, the present invention relates to a shadow mask having a structure capable of preventing the formation of foreign material, and preventing any foreign material that does form, from falling from the plate member and interfering with the manufacturing process.
Usually, a shadow mask is manufactured from an original metal plate material or member, hereinafter called a xe2x80x9cplate memberxe2x80x9d. The plate member is composed of a shadow mask body and an outer frame member to which the shadow mask body is supported through a plurality of connecting portions. The shadow mask body is formed, through an etching process, with an outer peripheral line penetrating through the plate member. Then, the outer frame member is removed through bending or pulling (tensioning). The outer peripheral line of the shadow mask is formed through etching, and plural connecting portions are formed intermittently as non-penetration portions. The shadow mask body is supported by the outer frame member of the plate member through such connecting portions.
The outer frame member is broken and then removed from the plate member by folding and bending the outer frame member or applying tension thereto, thus obtaining the shadow mask.
The shadow mask is then subjected to various processes, and thereafter, is mounted to a Braun tube.
Incidentally, in this specification the term of xe2x80x9couter peripheral linexe2x80x9d is defined as a line of the extremely outer peripheral portion of the shadow mask, which is formed by the etching process, irrespective of a shape of the extremely outer peripheral portion.
Japanese Patent Publication No. SHO 63-888, Japanese Patent Laid-open Publication No. HEI 4-71138, Japanese Laid-open Patent Publication No. HEI 8-31317 and Japanese Laid-open Patent Publication No. HEI 11-73876, disclose methods of manufacturing a shadow mask by removing the shadow mask from a plate member to which a shadow mask body is formed. The conventional methods prevent deformation of an effective portion of the shadow mask and effectively remove the outer frame member by effecting a half-etching process to the connection portions so that the connection portions are easily broken to remove the outer frame.
However, in conventional shadow mask manufacturing methods, the connection portions include a convex (protruding) shape at a position outside the outer peripheral line of the shadow mask. Such a protruding portion may negatively affect processes performed on the shadow mask after the removing process of the outer frame member or portion.
For example, in a process of pressing the shadow mask to form a predetermined shape which fits a Braun tube, the protruding portion of the connection portion may contact a metallic mold of the press and fall as a foreign particle (e.g., a metal piece or tip), and if the shadow mask is mounted to the Braun tube while a foreign particle adheres to an etching hole of the shadow mask, the quality of the Braun tube will be degraded.
An object of the present invention is to eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a shadow mask having a structure that, when the shadow mask is mounted to a Braun tube, foreign particles are either not formed, or are prevented from falling. A further object is to provide a plate member for such shadow mask and to provide a method of manufacturing the shadow mask.
These and other objects of the present invention can be achieved by providing, in one aspect, a shadow mask formed from a plate member comprising an outer frame portion, a body portion of a shadow mask having an outer peripheral line formed through an etching process and a plurality of connection portions through which the body portion of the shadow mask is supported by the outer frame portion, the shadow mask being formed by removing the outer frame portion from the body portion of the shadow mask, wherein a break portion is formed to the shadow mask by removing the outer frame so as to be recessed inward from the outer peripheral line of the shadow mask.
In preferred embodiments of this aspect, the break portion is formed by applying a half-etching process to a predetermined portion of the body portion of the shadow mask. The break portion is formed through one of breaking processes at least including a folding process, a tensioning process and a tearing process. The break portion has an end portion formed to be recessed inward from the outer peripheral line with a distance being set within a range from 10 to 100 xcexcm.
According to this aspect of the present invention, since the break portion formed by removing the outer frame portion is concavely formed inside the outer peripheral line of the shadow mask, it is possible to prevent, in a predetermined process after the removing process, the break portion from being rubbed and fallen from the shadow mask as a foreign particle.
In addition, since the half-etched portion has a remaining thin thickness, even in a case of folding the outer frame portion to break the outer frame portion, it is hard to cause cracks, making it possible to prevent a foreign particle from being fallen.
Furthermore, since the break portion is concavely formed (recessed) inward with respect to the outer peripheral line, it is possible to increase the degree of freedom to select one of the methods of removing the outer frame portion, thereby effectively manufacturing the shadow mask.
Since the end portion of the break portion is recessed inward from the outer peripheral line so that the distance between the end portion of the break portion and the outer peripheral portion is set within a range from 10 to 100 xcexcm, it is possible to prevent the metallic particle from being rubbed against another member and then fallen.
In another aspect of the present invention, there is provided a plate member for a shadow mask comprising:
a shadow mask body having an outer peripheral line providing an outline thereof, the outer peripheral line being formed through an etching process;
an outer frame portion for supporting the shadow mask body;
a plurality of connection portions through which the shadow mask body is supported by the outer frame portion; and
a portion to be broken formed on a shadow mask side at a portion inside the outer peripheral line of the shadow mask body.
In a preferred embodiment of this aspect, the portion to be broken is arranged so as to be opposed to the connection portion. The portion to be broken has a predetermined length in a direction along the outer peripheral line, the predetermined length of the portion to be broken being substantially the same as that of the opposed connection portion in the direction along the outer peripheral line. The portion to be broken is subjected to a half-etching process. The portion to be broken is formed with an intermediate portion having a substantially concave shape.
The portion subjected to the half-etching process has a width in a direction orthogonal to the direction of the outer peripheral line, and a center line of the width is located inside the outer peripheral line so that a distance between the outer peripheral line and the center line is longer than 25 xcexcm and not more than 100 xcexcm.
The portion to be broken is a portion forming a break portion of the shadow mask from which the outer frame portion is removed.
According to another aspect of the present invention, since the portion to be broken, which is broken when removing the outer frame portion, is formed on a shadow mask side with respect to the connection portions and an inner side of the outer peripheral line of the shadow mask, the break portion is concavely formed on an inner side of the outer peripheral line of the shadow mask. As a result, it is possible to prevent, in a predetermined process after the removing process, the break portion from being rubbed against another member so as not to be fallen as foreign particle.
Furthermore, since the predetermined length of the portion to be broken is the same as that of the opposite connection portion in the outer peripheral line, the break caused by removing the outer frame portion occurs selectively just inside the connection portion, that is, an inner side of the shadow mask, so that it is possible to form the break portion on an inner side position with respect to the outer peripheral line of the obtained shadow mask.
In addition, the outer frame portion is selectively broken at the half etched portion so as to be removed from the material sheet. The center line of the width is located on the inner side of the outer peripheral line so that the distance between the outer peripheral line and the center line is longer than 25 xcexcm and not more than 100 xcexcm, so that even if the break portion is removed through one of the folding process, the tensioning (drawing) process and the tearing process, it is possible to form the break portion inside the outer peripheral line of the obtained shadow mask.
In a further aspect of the present invention, there is also, provided a method of manufacturing a shadow mask comprising the steps of:
preparing a plate member comprising a shadow mask body having an outer peripheral line formed through an etching process, an outer frame portion for supporting the shadow mask body, a plurality of connection portions through which the shadow mask body is supported by the outer frame portion, and a portion to be broken formed on a shadow mask side at a portion inside the outer peripheral line of the shadow mask body;
removing the outer frame portion from the plate member through one of the breaking processes at least including a folding process, a tensioning process and a tearing process which is applied to the portion to be broken.
In this aspect the plate member may be produced from a metallic thin plate by effecting an etching process thereto.
According to further aspect of the present invention, the outer frame portion of the plate member is removed therefrom through one of the folding process, the tensioning process and the tearing process, it is possible to easily manufacture the shadow mask capable of preventing the break portion from being rubbed against another member so as not to be fallen as a foreign particle.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.